Separation of trimethyl amine and ammonia from amination reaction mixtures



J. F. OLIN SEPARATION OF TRIMETHYL AMINE AND AMMONIA Filed Feb. v26 1945 #VVE/10U@ Patented Oct. 30,1945

2,388,2174 SEPARATION OF TRIMETHYL AMINE ANDk AMMONIA FROM AMINATION REACTION John F, "01m, Grosse ne, Mien, signor to `Sharples,Cl1emicals Inc., Philadelphia, Pa., a

corporationlof Delaware original application september 2, 1942, serial Np.

` 457,053; Diyided and this application 26, 1943, Serial No.v 477,268

February The present inventionpertains toj separation ofV ammonia and trimethyl amine from each other and from other constituents obtained in the mixture resulting from alkylation of ammonia and lower methyl amines. Reaction mixtures resulting from alkylation of ammonia .by cata-lytic remethyl amine and/or dimethyl 'amine prior to` any attempt to separate these constituents from action thereof in vapor phase with methanol or methyl etherordinarily contain all three of the Y methyl amines and also contain a considerable quantity oi ammonia. The present invention is concerned with the separation of ammonia. and

trimethyl amine from reaction mixtures of this j type and from other mixtures containing-said constituents. This application is a division of my prior application Serial No. 457,053, led September 2, 1942, for Purification of amine reaction mixtures.

As is well known to those skilled in the art, the separation oi' ammonia and trimethyl amine from reaction mixtures containing these constituents and from each other is complicated and rendered dimcult =by the fact that ammonia forms with trimethyl amine a constant boiling mixture. While all of the trimethyl amine may be removed from a crude reaction mixture containingthe three methyl amines and ammonia by the simple procedure of adding suicient ammonia to carry on all oi' the trimethyl amine in the i'orm of a constant boiling mixture with ammonia, such procedure leaves unsolved the problem of separating the trimethyl amine of the constant boiling mixture `from the ammonia.

P'Ihe present invention provides a procedure by which this separation may be 'eiiciently accomplished, and it also provides procedure by which ,ammonia which iis-separated from the trimethyl amine is returned to the distillation step to assist in carrying overhead a further quantity of trimethyl amine. After all of the trimethyl amine has been removed by continued operation in this ner, the ammonia maybe maintained in vapor Y manner, the remaining amines and ammonia of tracted by an aromatic hydrocarbon solvent to tion, la mixture eilect selective solution of the trimethyl aminein that solvent. While any aromatic hydrocarbon solvent having the desired selective solventy power may be employed in the practice of the invention, thel preferred solvents are xylene, toluene and benzene. The aromatichydrocarbon solvent may be mixed with the reaction mixture containingvammonia, trimethyl amine, monoeach other by distillation, and the ammonia distilled from the resulting solution containingtrimethyl amine dissolved in the aromatic hydrocarbon, but this method of operation is less efiicient than my preferred embodiment, which involves passage of ammonia and trimethyl airline overhead asia constant boiling mixture from higher boiling constituents of the reactionmixture. When the ammonia and trimethyl amine are first passed overhead as a constant boiling mixture, they may be contacted in counter-now relationship with the extracting aromatic hydrocarbon solvent by passage upwardly in vapor phase through a distillation column in countercurrent relationship to a descending liquid phase stream of the solvent. By operating in this manphase and returned to the initial step of distillation tol assist rin carrying overhead a further quantity of trimethyl amine, while the solution of trimethyl amine in aromatic hydrocarbon passes to the base of the second column'and is thence passed to a further distillation column in which the trimethyl vamine may be separated f from the aromatic hydrocarbon solvent.

The detailed nature of the invention and the preferred/ means for practicing4 it will be better evident rfrom consideration of the following detailed description in the light of the attachedflow sheet, in which the single iigure illustrates the practice ofthe invention as applied in separation lfrom each other of a mixture containing monomethyl amine, di-methyl amine, tri-methyl amine and ammonia. i

As illustrated in the iiow sheet, the reaction Y mixture containing trimethyl .amine and am- 4 1 monia and also containing mono-methyl amine, y

di-methyl amine or both, is -rst passed tothe distillation column Ill, which is provided with a' f' pot II. Ammonia is also passed to this column and carries trimethyl amine contained in the reaction mixture reachingthe column III overhead in the `form of an azeotropic mixture. 'I'he mix-1 ture'passing overhead from column I0 is passed to a condenser I2, from which condensate is returned through the redux meter I3 to the top of the column I0. The condensed mixture -oi' trimethyl amine and ammonia is passed through valve I 4, vaporizer I5 and meter I 6 to a central portion of `a scrubbing column II. An aromatic hydrocarbon which is a selective 'solvent for the vtrimethyl amine passed to column I1 is introduced toward the top o1' that column, xylene.

toluene and benzene being the preferred solvents. Xylene from tank I8 may be passed by pump I9 into the top of distillation column I1, as illustrated. The xylene extracts the major portion of the trimethyl amine from its mixture with ammonia during descent of the xylene through the column, the ammoniaapassing overhead through valve 2li. to condenser 2| from which it may be passed to receiving tank 22 and. ultimately returned to the moti I by pump 23, to assist in carrying overhead a further quantity of trimethyl amine from the material introduced into the column Il) for treatmenttherein. The overhead fraction from column I1 contains a very small proportion of trimethyl amine, and return of the overhead fraction to the pot Il is desirable inV order that this trimethyl amine may be recovered, in addition to the advantage aiforded by such return in .assisting in removal of trimethyl amine overhead from columnIl.

'I'he solutionof trimethyl amine in xylene obtained by the scrubbing operation in the column I 1 is passed from the base of that column through valve 24 to acolumn 25, where the trimethyl amine is separatedirom the xyIene by distillation, the xylene being passed as al condensate through cooler 25 and ,valve 21 tothe xylene storage tank Il, while-.the trimethyLamine is passed overhead .through valve 28 and condenser 29 to the crude .trimethyl amine receiving tank 30. The trimethyl `amine'fraction passed to the receiver 30 will contain a small proportion of ammonia, and it 'is preferably redistilled to provide an ove'rhead fraction consisting of an azeotropic mixture of ammonia and trimethyl amine, with substantialhtpure trimethyi amine as the distillation residue.

Best results in operation of the process as described above have been attained in cases in which the colimn I was Operated as a continuous distillation column under a. gauge pressure of 250 pounds per square inch, the column I1 operated' as a continuous scrubbing column under a gauge pressure of 200 pounds per square inch, and the column 25 operated at a gauge pressure of 50 pounds-per square inch. The pressure in the column -.,|1 may be regulated by adjustment 'of the valve-2li andthe-'pressure in the column 25 by adjustment [of the valve 28. The liquid levels in the columns I1 and 25 may be maintained substantially constant during the continuous extracting and distillation operations by the l valves 24 and 21, respectively.

After removal of the trimethyl amine and ammonia in the manner described above, the monoand di-methylamines and ammonia remaining in the pot II may be separated from each other by distillation.

.x Y Example v323 pounds of a crude methyl amine mixture, containing -mono-, di. and tri-methyl amine,

together with ammonia., were obtained by oata-A v lytic reaction between methanol and ammonia,

followed by preliminary distillation of theresulting reaction mixture. This crude methyl aminel passed through vaporizer I5 to scrubber I1, which was maintained at about 225 C. Xylene was continuously fed to the top of the scrubbing column I1 as illustrated on the flow sheet. Operationv was continuously conducted under these conditions, with removal of ammonia overhead through condenser 2| until concentration of the trimethyl'amine in the distillate from the column In dropped to 5%. When this condition was reached, feed of further reaction mixture to the column III was discontinued, and the remaining material in pot Il was fractionally distilled. The following cuts were obtained as the result of this distillation:

Cut No. Donnas Material so. s NH. containing 6% (CH'mN. 26. 5 NH; and CHiNHg.

a4 CHiNHi (98% pure)- 45. 5 CHiNHa and (CHINH. 89. 5 (CHlNH (99+% Pure).

During the scrubbing operation performed in the column I1, the solution of trimethyl amine in xylene removed from the base of this column was passed continuously to column 25, where it was distilled to separate the trimethyl amine from the xylene. The overhead fraction of this distillation, consisting of 154 pounds oi' product analyzing about 4% ammonia and 96% trimethyl amine was collected in receiver 30.

Various modifications are possible within the scope of the invention, and I do not therefore wish to be limited except by the scope ot the fpllowing claims.

I claim:

l. In the separation of ammonia from a mixture containing ammonia and trimethyl amine, the process comprising selectively extracting trimethyl amine from the mixture by dissolving said trimethyl amine in an aromatic hydrocarbon solvent chosen from the class consisting of xylene, toluene and benzene and separating ammonia from the resulting solution by distillation.

2. In the separation of ammonia and trimethyl amine from a mixture containing them, and from each other by steps including distilling a constant boiling mixture of ammonia and trimethyl amine overhead from higher boiling constituents, the process comprising selectively extracting trimethyl amine from the mixture thereof with ammonia passed overhead by dissolving said trimethyl amine in an aromatic hydrocarbon sol-4 vent chosen from the class consisting of xylene, toluene and benzene and separating ammonia from the resulting solution by distillation;

3. A process as defined in claim 1, in which the selective extraction of the trimethyl amine is accomplished by passing a vapor phase mixture of the trimethyl amine and ammonia in countercurrent relationship to a descending stream of the aromatic hydrocarbon solvent in a distillation column.

4. In the separation of ammonia and trimethyl amine from a mixture containing them, and from each other by steps including distilling a constant ammonia, to the column I0, and trimethyl amine was distilled overhead from this,l column, to-

gether with the ammonia, as an aze'otropic mixture. A good reflux was maintained inthe'col-v boiling mixture of ammonia and trimethyl amine overhead from higher boiling constituents, the process .comprising selectively extracting trlmethyl amine from the mixture thereof with ammonia passed overhead by passing said overhead mixture in vapor phase in counter-current relationship to a. descending stream of an aromatic mixture of ammonia and trimethy1 amine was 75 hydrocarbon solvent chosen from the class con.

ammonia and trimethyl amine overhead from said other methyl amine, the process comprising selecl tively extracting trimethyl amine from the mixture thereof with ammonia passed overhead by passing said overhead mixture in vapor phase in counter-current .relationship to a descending `3 stream oi an aromatic hydrocarbon solvent chosen from the class consisting o! xylene, toluene and lbenzene ina distillation column.

6. In the separation oi ammonia from a. mixture containing ammonia and trimethyl amine,

the process comprising selectively extracting trimethyl amine from the mixture by dissolving said trimethyl amine in an aromatic hydrocarbon solvent chosen from the class consisting of xylene. toluene and benzene and separating ammonia l from the resulting solution.

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